Nowadays, the consumer electronic products are generally provided with an advanced display as a basic device. A liquid crystal display (LCD) with high resolution and colorful screen has been commonly used in the consumer electronic products, such as cellular phone, digital camera, computer monitor, or laptop PC.
A shift register is an essential part of a driving circuit in the LCD panel. The shift register is used to drive a plurality of stages of displaying circuit in the LCD panel. Hence, the quality of circuit design for the shift register determines the performance of the LCD panel. Referring to FIG. 1, a circuit diagram of a stage of shift register 11 in a conventional LCD is shown. The shift register 11 includes a plurality of transistors 16, 17, 18, 19, 20, and 21 for controlling an output signal OUTPUT1 according to clock signals C1 and C2. Further referring to FIG. 2, a signal waveform diagram of each node in the shift register 11 is shown. The transistor 20 is turned on when the clock signal C1 is in a high voltage level, thereby an node P2 is in a VDD voltage (high voltage level) for turning on the transistors 17 and 19 simultaneously. Therefore, the voltage levels of the gate (i.e. the node P1) and source of the transistor 16 are both pulled down to a VSS voltage (low voltage level).
Although the shift register 11 of conventional LCD can rapidly pull down the voltage levels of the gate and source of the transistor 16 to the VSS voltage, the DC voltage source VDD is required to be provided in the shift register 11. The transistors 18 and 20 may be induced a stress by connecting to the DC voltage source VDD all the time. Furthermore, the present shift register circuit design of LCD is required to be provided without the DC voltage source VDD for reducing manufacturing costs and improving device performance. Therefore, there is a need to provide a novel shift register without the DC voltage source VDD to resolve the above problems in conventional LCDs.